2 2*x - 18
2*x^2 - 1*18
1*(x + 3)*(x - 3)
(1*(x + 3))*(x - 3)
-18.0 + 2.0*x^2
2*(-3 + x)*(3 + x)
/ 2\ 2*\-9 + x /
2*(-9 + x^2)